1. Field of Invention
The invention relates to the field of preparing medical solutions, in particular solutions for infusion and renal substitution therapy. The subject matter of the invention is a bag, in particular a multichamber bag for holding concentrates with a circumferential seal and a holding area made of a flexurally rigid material surrounding the feed ports and/or withdrawal ports for fluids.
2. Description of the Prior Art
Dialysis fluids for hemodialysis or peritoneal dialysis as well as fluids and replacement fluids for hemofiltration processes typically contain dissolved substances, for example:                electrolytes Na, K, Mg, Ca to maintain an acceptable electrolyte balance in the patient        buffers (for example, bicarbonate, acetate, lactate, etc.)        glucose (or other osmotic agents) as osmotic agents in peritoneal dialysis or for maintaining the blood sugar level during hemodialysis and hemofiltration        acids or salts of acids (for example, HCl and/or Cl−, acetic acid and/or acetate, citric acid and/or citrate) which might contribute toward the neutralization of basic partial dialysis solutions or are present as counterions in electrochemical equilibrium.        
The substances used for dialysis solutions cannot usually be stored in a ready-to-use mixture because these substances can cause mutual degradation. The required stability of a component in storage may presuppose storage conditions that would lead to degradation of other components. One example is glucose, which can be stored for a lengthy period of time only in a certain acidic pH range, depending on the concentration of the glucose in solution, without being subjected to unwanted degradation processes to an excessive extent. At the same time, the compound sodium bicarbonate, which is often used as a buffer in dialysis solutions, cannot be stored under such acidic conditions because, depending on the pH, bicarbonate tends to decompose and can release CO2. Under decomposition conditions, the concentration of bicarbonate changes, which is unacceptable from a therapeutic standpoint. The rising CO2 partial pressure also makes demands of the medical dialysis machines leading to technical problems.
A variety of alternative compositions, storage conditions and dosage forms of dialysis solutions or concentrates are known which permit long-term storage. It is known that the solution components are divided into a combination of partial solutions or concentrates so that only compatible components of a partial solution or of a partial concentrate are stored together. For the solutions used in peritoneal dialysis, a first partial solution comprising glucose, which assumes the function of the osmotic agent, is typically stored at an acidic pH together with additional electrolytes, for example, sodium, calcium, magnesium. Another basic or buffered partial solution is necessary to supply a physiological mixed solution or at least a mixed ready-to-use solution of the first part and the second part with the first acidic partial solution for treatment. The second part often consists of a solution or a concentrate of sodium bicarbonate and sodium chloride. The partial solutions or concentrates are present in several containers or in several compartments of one container. The partial solutions or partial concentrates are present separately, so that there is no mutual influence. Immediately prior to use of the dialysis solution, the separate partial solutions or partial concentrates are mixed, possibly with the addition of other aqueous components and are prepared for the treatment.
In hemodialysis, partial solutions or partial concentrates are often present in the dialysis machine and are mixed during the course of the treatment to prepare a finished dialysis solution. Partial concentrates in solid or liquid form are often used for this purpose; these concentrates are present in individual containers and are diluted by connection to the dialysis machine with the help of a prepared hydraulic solution and then are processed to yield the finished ready-to-use dialysis solution.
Other developments in dialysis have tended toward supplying the necessary concentrates in a single container. First, this simplifies the production and handling of the containers but secondly this also simplifies the hydraulic system of the dialysis machine because then only one holding unit for the partial solutions or concentrates need be provided and fewer connections are necessary to process the solution through the hydraulic system. This trend can be observed in particular in acute dialysis because a greater mobility of the treatment systems is demanded there.
In another variant, dialysis solutions for hemodialysis are not prepared from concentrates during the course of the treatment but instead the total required volume of the dialysis solution is prepared in one batch in a step prior to the treatment. The batch is stored in a tank which is prepared for connection to a dialysis machine. In many cases, the tank is an integral component of a dialysis treatment unit or in certain cases it may also be moved separately from the latter. Batch dialysis may thus offer the advantage that the treatment site can be selected relatively independently of location through the one-time preparation of the batch. Thus treatment stations at various locations can be used without having to rely on a dialysis solution preparation unit or a water connection which supplies the necessary water for diluting the concentrates. In these cases, the dialysis solution is mixed from concentrates on an apparatus provided for this purpose and then is stored, usually in a portable tank.
Large-volume liquid bags, which are understood below to be bags having a capacity of at least 5 liters, are subject to special mechanical requirements. The film material of the bags must have an impact strength that is high enough so that the bags will not rupture if they fall. These requirements are demanded at low temperatures in particular. Corresponding suitability tests have assessed the strength of solution bags in a fall test. In this test, bags first regulated at a temperature of 4° C. are dropped to the floor from a height of 2 meters in a room regulated accordingly and any rupture behavior of the bags that occurs is evaluated. In addition, the welds of the bags which are assembled from film sections must be able to withstand certain compressive stresses without resulting in leakage of the bag. The bag materials must also meet additional requirements of heat sterilizability and transparency. These requirements are relevant for solution bags in particular which are marketed and distributed in sterilized and ready-to-use form. The mechanical stresses to which such bags are exposed on the distribution routes result in complaints and unpleasant follow-up demands on the part of customers to the manufacturers. Solution bags for peritoneal dialysis, hemodialysis and hemofiltration are conventionally available in sizes of up to five liters.
It is still difficult to supply large-volume solution bags in a ready-to-use form because of the transportation logistics. For bags which are used in batch dialysis as described above, the solutions must be prepared at the treatment site and at the site of use. The bags must thus be filled on-site by a suitable fluid processing installation and can be used within the hospital ward, and to a certain extent also regionally beyond that. Such batch systems may require bag volumes of 30 to 120 liters. Such large-volume bags already have a heavy load on welded sections, e.g., the welded seams or ports welded into the bags, due to their inherent weight.
To be able to fill or empty a bag through a port, these ports must be incorporated into the circumferential weld which secures the film wall sections against one another and defines an internal volume of the bag. The ports have a through-opening connecting the inside of the bag to the outer area so that fluid can flow through it. The outer end of the port is connected to additional lines or connections of the bag system of the treatment station. It is known that the welded area of the ports should be designed in particular for the welded connection to the film material. Therefore so-called welding ribs have been developed, running the transverse direction to the direction of extent of the through-opening of the ports and running parallel with the weld of the film. During the manufacturing process, welding tools press the films against these relatively thin welding ribs, resulting in a very high contact pressure locally, which seals the weld.
Beyond the simple sealing, however, these joints must also establish a fixed mechanical connection between the film and the port. It is customary in many cases for the bag to be supported by means of holders at the welded ports or in a suspended position. Depending on the volume of the respective filled bag, the film exerts high tensile forces on the weld due to the gravitational force of the material forming the filling. For large-volume bags, the technical requirements for establishing the described weld in a sealing and load-bearing manner would be too high to manufacture a bag system with acceptable manufacturing costs in mass production.
The tensile forces acting on the film walls due to the gravitational force and possibly the internal hydrostatic pressure of a filled large-volume bag on the film walls may lead to thinning of the film material. The film wall yields to the tensile forces because of plastic or elastic deformation. Films may be designed to be stable accordingly despite these deformations. Reference is made in particular to WO 2011/128185, the content of which is herewith referenced explicitly. This document describes an elastically extensible film which is provided for producing a large-volume bag.
One problem that occurs in mechanical stressing of welded sections on large-volume bags, is that the film may become detached from its welded connection with the welding ribs of the welding boat due to thinning. Such an effect may occur in particular because the film material must be stretched over the curved welding ribs of the welding boat for the welding operation. In addition, film-stretching forces also act on this welded location due to the force of gravity or the hydrostatic pressure of the filled bag.
It is also desirable for such plastic parts to have functional designs such as holding sections for access ports to the bag or a holding device to which the bag can be attached. These use requirements also necessitate the use of a mechanically stable, flexurally rigid material.
EP 1 554 177 discloses a method for sealing and welding tubing ports in place between the film walls of the solution bag. This document refers to mechanical gripping of the film, insertion of the tube port and then welding. The problems of film elongation are discussed, but this document does disclose a plastic part made of a flexurally rigid material.
EP 1 438 090 discloses bag having two access ports, each of which opens into two separate internal areas of the bag. The bag has a holder consisting of simple receiving holes in the film material. Such a holding device is not suitable for large-volume bags because the film material can tear under the load of the filled bag.
EP 1 642 614 B1 discloses a concentrate bag with a plastic part, which is prepared functionally for adding/removing fluid and which assumes the holder function of the bag. The plastic part is welded to the film walls in a sealing manner via welding ribs. The bag holds a concentrate for preparing a saturated solution, with which a dialysis fluid can be prepared. On the whole, the bag has only a low weight, even in the filled state, so that the problems of ensuring the sealing function and holding function of the welding zone of the welded hard part are not important.
U.S. Pat. No. 4,386,634 discloses a large-volume container in which dry concentrates are placed for preparing a dialysis solution. A liquid concentrate is prepared by adding water. The embodiment of the connection between the film wall and the hard part is not described in detail from the standpoint of the fastening and sealing.